1. Field of the Invention
This invention relates to a process for inserting sealing strips in subterranean an curtains or barriers between the walls of underground trenches which trenches are packed with bentonite or similar packings.
2. Description of the Prior Art
Subterranean an curtains are of great importance for the sealing of receptacles or terrain carrying or holding water or the sealing of water-bearing strata. Subterranean curtains are constructed by excavating trenches, and simultaneously filling them with support compounds such as bentonite. A solidifier, e.g. cement, can also be added to the bentonite. Such subterranean curtains offer a certain degree of sealing. For requirements beyond what they can provide, in particular for the sealing of waste dumps, the subterranean curtains or trenches are equipped with sealing strips. The sealing strips are lowered into the bentonite suspension. The connection of the sealing strips on their edges presents a problem. In the past, a number of proposals have been advanced for the connection of the edges of the strips. These proposals are based on joint strips, which are welded to the strip edges, and are inserted in one another while the sealing strips are lowered. The joint strips are complicated and expensive to install and handle. German Patent Application No. 37 12 722.5 therefore proposes that the sealing strips no longer be lowered in the longitudinal direction, but be laid out along the excavated trench, and in this position, the individual strips are welded together, until one whole strip is formed, which has the same width as the depth of the trench. For the customary trench depth of 30 m, for example, the width of the strip assembled in this manner would also be 30 m. The strip is to be lowered at the same time as the welding takes place. It has so far not been possible to implement this proposal, however, since trenches 60 m and longer cannot yet be made in one piece. In the prior art, trench walls have had to be manufactured in segments, whereby the maximum segment lengths possible are 5 m, depending on the support medium or resulting structure selected. Without a support medium or structure, a trench wall would have only a very low strength to resist ruptures. In other words, without a support medium, only very shallow or short trenches have been made. With a support medium, of course, the length cited above can be achieved, but that already requires that the bentonite slurry suspension or mixture contain significant amounts of bentonite. Such a bentonite suspension is very difficult to produce. It is produced by mixing the bentonite with water in conventional mixing drums. The higher the bentonite content, the more difficult the mixing becomes. An example of the slurry trench method is found in U.S. Pat. No. 4,696,607 entitled "Slurry Trench Method and Apparatus for Constructing Underground Walls". This document is herewith incorporated by reference as if the entire content thereof was set forth herein in its entirety.
Additional problems result with the introduction of the sealing strips in bentonite suspensions with a high concentration of bentonite. Such bentonite suspensions are very tough and difficult for the sealing strip to penetrate. They have a high moment of resistance to the introduction of the sealing strips.
Related to the proposal to lower very long sealing strips into the trenches in the ground was the proposal that a welding of the conventional type be performed on the edges of these sealing strips. The sealing strips are preferably made of steel or another weldable material. In the event that an epoxy or metal or other glue is to be used even non-metal sheets can be used. The strips are preferably of a thickness to be easily bendable in use in the exercise of the invention. In other words, the edges of the long sealing strips were to be connected to one another by overlapping welds or web welds with proven welding equipment and proven techniques. To make the weld joint possible, it was specified that the overlapping region of the sealing strips was to be surrounded by a two-piece housing, whereby one housing part would be located on the the one side of the strip and the other housing part on the other side of the strip. The housing parts have seals in the region where they contact the sealing strips, and are pumped out, so that the overlapping strip edges are readily accessible for flushing and welding. The use of the housing, including the flushing and pumping out, was considered so expensive that the use of this process seemed limited only to extremely long sealing strips.